part 2] OF THE LLANGOLLEN DISTEICT. 225 



Ashgillian affinities of the fauna in the succeeding heds, the 

 determination of the precise horizon of the shales would probably 

 throw some light upon the relation of the Ashgillian to the 

 Hartfell Group. A curious feature of the Upper Ashgillian fauna 

 was the association of Meristina crassa, formerly regarded as a 

 distinctive Lower Llandovery fossil, with undoubted Ordovician 

 trilobites, such as Chas?noj)S. In Britain such an association was 

 apparently found only in this district, and it might help towards 

 the comparison of the strata near the Ordovician -Silurian boundary 

 in Wales and in Norway where Prof. Johan Kiaer had united the 

 Meristiiia-crassa Beds with the Ordovician. 



The brachiopods of the Valentian to which Dr. Wills had 

 referred were unfortunately very poorly preserved, and did not 

 afford as much help in the subdivision of the series as one would 

 like. 



The structure of the region was extremely interesting, and was 

 quite unusual for Wales. It seemed probable that the deviation 

 of the folds from the usual north-east and south-west into the 

 east-and-west direction was accounted for by the region being 

 beyond the protective influence of the rigid masses of North Wales, 

 and that the rocks had therefore been wrenched out of their usual 

 direction. It was not, therefore, surprising that the Authors had 

 found evidence of considerable torsional structures and lateral 

 movement in the district. 



The terms used in describing- some of the structural elements 

 appeared to have a theoretical implication which Avas not quite 

 clear. Such were the ' nodal anticline ' of Myn3^dd-Cricor and 

 Cyrn-y-Brain and the ' Corwen anticlinal buttress.' He would 

 like to know what was implied by the term ' nodal anticline ' and 

 AV'liat was its influence upon the structure. The expression 

 ' buttress ' appeared to imply that it had in some manner influenced 

 the folding of the adjoining country ; whereas it seemed clear that 

 this anticline was the result of the same folding movement as that 

 which affected the rest of the counfay, but that the stresses in the 

 eastern region are different from those on the west. 



Dr. T. T. Geoom said that he had listened with great interest to 

 Dr. Wills's lucid description of the Authors' work on the district. 

 The structure, at any rate of the southern part of the area, with 

 which alone he Avas familiar, Avhile of much apparent simplicity, 

 was in reality far from simple, and the Authors Avere to be con- 

 gratulated on the achievement of a notable piece of Avork. The 

 speaker Avas gratified by Dr. Wills's generous appreciation of his 

 joint Avork Avith Mr, Lake, and by the close agreement Avith this of 

 the Authors' independent researches. There seemed, indeed, to be 

 few points of difference. He would like to ask the Authors 

 Avhether they had been able to prove definitely the identity of the 

 Glyn and Corwen G-rits, which Mr. Lake and himself had left an 

 open question ; and to have fuller evidence of a continuity of 

 deposition betAveen the Ordovician and the Silurian deposits, since 

 some of the facts seemed to be rather in faA^our of a break. With 

 Q. J. d. S. No. 310. Q 



